Complexation and removal of mercury from flue gas desulfurization systems

ABSTRACT

A method for the reduction and prevention of mercury emissions into the environment from combusted fossil fuels or off-gases having mercury with the use of hypoiodite is disclosed. The hypoiodite is used for the capture of mercury from the resulting flue gases using a flue gas desulfurization system or scrubber. The method uses hypoiodite in conjunction with a scrubber to capture mercury and lower its emission and/or re-emission with stack gases. The method allows the use of coal as a cleaner and environmentally friendlier fuel source as well as capturing mercury from other processing systems.

TECHNICAL FIELD

This invention relates to the reduction of mercury emissions into theenvironment from the combustion of coal and/or other carbon-based fuelsas well as from other processing systems. The invention relates to themethod of capturing mercury from flue gases by flue gas desulfurizationsystems or scrubbers thereby reducing the levels of toxic mercury, whichenables the use of coal as a clean and environmentally friendlier fuelsource as well as makes other processing systems more environmentallydesirable.

BACKGROUND

The demand for electricity continues to grow globally. In order to keepstride with the growing demand, coal continues to be a primary sourcefor electricity generation. The burning of coal in power generationplants results in the release of energy, as well as the production ofsolid waste such as bottom and fly ash, and flue gas emissions into theenvironment. Emissions Standards, as articulated in The Clean Air ActAmendments of 1990 as established by the U.S. Environmental ProtectionAgency (EPA), requires the assessment of hazardous air pollutants fromutility power plants.

Conventional coal-fired combustion furnaces and similar devices produceemissions that include pollutants such as mercury. Mercury vapor cancontribute to health concerns. At the levels common in the atmosphere,the concentrations of mercury are usually safe. However, mercury canaccumulate in ecosystems, for example, as a result of rainfall. Someconventional systems attempt to control mercury emissions withparticulate collection devices.

The primary gas emissions are criteria pollutants (e.g., sulfur dioxide,nitrogen dioxides, particulate material, and carbon monoxide). Secondaryemissions depend on the type of coal or fuel being combusted but includeas examples mercury, selenium, arsenic, and boron. Coal-fired utilityboilers are known to be a major source of anthropogenic mercuryemissions in the United States. In December of 2000, the EPA announcedits intention to regulate mercury emissions from coal-fired utilityboilers despite the fact that a proven best available technology (BAT)did not exist to capture or control the levels of mercury released bythe combustion of coal. This has been further complicated by the lack ofquick, reliable, continuous monitoring methods for mercury.

Mercury (elemental symbol Hg) is a metal that melts at 234K (−38° F.)and boils at 630K (674° F.). As such, it can be expected to have a highvapor pressure relative to many metals. The oxidized forms of mercury,Hg²⁺ and Hg⁺, have much lower vapor pressures and can be captured by flyash particulates.

Mercury is found in coals at concentrations ranging from 0.02 to 1 ppm.The mercury is present as sulfides or is associated with organic matter.Upon combustion the mercury is released and emitted into the flue gas asgaseous elemental mercury and other mercury compounds. The mercuryappears in the flue gas in both the solid and gas phases(particulate-bound mercury and vapor-phase mercury, respectively). Theso-called solid-phase mercury is really vapor-phase mercury adsorbedonto the surface of ash and/or carbon particles. The solid-phase mercurycan be captured by existing particle control devices (PCDs) such aselectrostatic precipitators (ESPs) and fabric filters (FF), the lattersometimes referred to as baghouses.

Several control strategies have been developed for the control ofmercury emissions from coal-fired boilers. Some of these methods includeinjection of activated carbon, modified activated carbon, variouschemical catalysts, and inorganic sorbents. Unfortunately, none of thesestrategies removes all the mercury from the flue gas. The efficienciesrange from as low as 30% to as high as 80% based on the amount ofmercury entering the system with the coal. In addition, thesetechnologies either produce unwanted effects on by-products such asimpacting the quality of fly ash, or they generate additional wastestreams for the power plant. Both lead to higher operational costs forthe power plant. One promising strategy is to take advantage of existingair pollution control devices (APCDs) to augment or to serve as theprimary means to remove vapor-phase mercury. Two examples of APCDs aresemi-dry and wet scrubbers or flue gas desulfurizer (FGD). Semi-dry FGDsare also known as spray dryer absorbers (i.e., SDAs), circulating dryscrubbers (CDS), or TURBBOSORP® available from Von Roll.

Sulfur oxides (SO_(x)) regulatory compliance mandates the use of atleast one of several control strategies. Three such strategies that areused in the US are sorbent injection into the flue gas following by aparticulate collection device such as an ESP or a FF, and wet or dryflue gas desulfurizers. At present, about 3% of the coal-fired powerplants are using sorbent injection. FGD scrubbing accounts for 85% usingwet and 12% using dry scrubber technologies. Wet scrubbers achievegreater than 90% SO_(x) removal efficiency compared to 80% by dryscrubbing. In wet scrubbers, the flue gas is brought into contact withslurry containing an alkaline source such as lime or limestone. TheSO_(x) is adsorbed into the water and reacts to form calcium sulfite. Ithas been demonstrated that simultaneous to SO_(x) capture, wet FGDs canbe used to capture vapor-phase mercury from the flue gas.

Elemental mercury is water-insoluble and is not removed by a wet FGD. Incontrast, oxidized mercury in the flue gas is water-soluble and isremoved. The Information Collection Request (ICR) mercury datademonstrated that ionic mercury is removed effectively approaching 90%by wet FGDs. Hence, one strategy for mercury capture is to oxidize allthe mercury during the burning of the coal and capture the oxidizedmercury in the wet scrubber. Work carried out by URS in conjunction withthe Department of Energy/National Energy Technology Laboratory(DOE/NETL) investigated just such a strategy. There are two criticaltechnical steps to the implementation of this strategy. The first is thecomplete oxidation of the vapor-phase mercury exiting the boiler and thecoal. URS, among others, is developing strategies and technologies toaccomplish this step. To date, they have demonstrated that independentof the coal type, vapor-phase mercury speciation can be shifted toextensively 100% oxidized mercury. The second critical technical step inthe implementation of this control strategy is the sorption of theoxidized mercury and removal in the wet scrubber. The problem,identified early on, is that there are reactions occurring in the wetscrubber liquor that reduce oxidized mercury to elemental mercury andlead to “re-emission” or release of elemental mercury into the scrubbedflue gas. The prevention of ionic mercury reduction in wet scrubberliquor has been studied and reported by G. M. Blythe and D. W. DeBerryat URS and others.

The findings have suggested that complexation of the ionic mercury isone way to reduce or eliminate the generation of elemental mercury inthe scrubber. This same study has demonstrated that not all chelants ofionic mercury can accomplish this in a wet FGD. In a recentpresentation, plant results of such a chelant, TMT-15,trimercapto-s-triazine, available from Degussa, were inconclusiveregarding the prevention of re-emission of mercury across a wetscrubber. Efficient and cost-effective apparatuses and methods forcontrolling emissions of mercury remain a desirable need in the artwhether from combustion sources such as coal plants and cement kilns orother sources such as incinerators used in a variety of activities.

SUMMARY

In one aspect, a method for reducing mercury emissions is disclosed. Inone embodiment, the method includes providing a gas stream comprisingmercury and passing the gas stream into a scrubber comprising a scrubberliquor and hypoiodite.

In one embodiment, the method includes burning a carbonaceous fuelcomprising mercury, thereby producing a flue gas, and passing the fluegas into a flue gas scrubber comprising a scrubber liquor andhypoiodite.

In some embodiments, the hypoiodite is mixed with a carrying agentselected from: limestone slurry, lime slurry, sodium-based alkalisolution, trona-based solution, sodium carbonate solution, sodiumhydroxide solution, and water.

In some embodiments, the method also includes mixing an iodine salt andan oxidant to form the hypoiodite. In some embodiments, the oxidant issodium hypochlorite.

In some embodiments, the mercury is from combusted coal. In someembodiments, the mercury is from an incinerator. In some embodiments,the mercury is from a cement kiln. In some embodiments, the mercury isfrom an ore refinery. In some embodiments, the mineral ore processed atthe refinery contains phosphorus (such as phosphate). In someembodiments, the mineral ore processed at the refinery contains gold.

In some embodiments, the scrubber is a wet scrubber selected from spraytower system, a jet bubblers system, and a co-current packed towersystem. In some embodiments, the hypoiodite is added to the liquor andthen added to the scrubber. In some embodiments, the hypoiodite is addedto the scrubber containing the liquor. In some embodiments, thehypoiodite is added to a virgin liquor then added to the scrubber. Insome embodiments, the hypoiodite is added to a make-up liquor then addedto the scrubber. In some embodiments, the hypoiodite is added to areturn liquor then added to the scrubber. In some embodiments, thehypoiodite is added to a reclaimed liquor then added to the scrubber. Insome embodiments, the hypoiodite is added to a liquor injected directlyinto flue gases then added to the scrubber. In some embodiments, thehypoiodite is added to a recirculation loop of the scrubber liquor. Insome embodiments, the hypoiodite is added to a low solids return to thescrubber from a scrubber purge stream. In some embodiments, thehypoiodite is added to an aqueous stream introduced into the scrubber.In some embodiments, the hypoiodite is added to a demister. In someembodiments, the hypoiodite is added to a make-up water stream.

In some embodiments, the mercury is from an incinerator. In someembodiments, the mercury is from a cement kiln.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of an experimental setup of impingers tomeasure simulated mercury emission capture.

FIG. 2 is a plot that shows the percent of mercury removal as a functionof sodium hypochlorite concentration with and without hypoiodite usingan embodiment of the invention.

DETAILED DESCRIPTION

Unless expressly stated to the contrary, use of the term “a” is intendedto include “at least one” or “one or more.” For example, “a device” isintended to include “at least one device” or “one or more devices.”

Any ranges given either in absolute terms or in approximate terms areintended to encompass both, and any definitions used herein are intendedto be clarifying and not limiting. Notwithstanding that the numericalranges and parameters setting forth the broad scope of the invention areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.Moreover, all ranges disclosed herein are to be understood to encompassany and all subranges (including all fractional and whole values)subsumed therein.

One of skill in the art would also understand that salts of iodine referto iodine ions typically seen as I⁻ but which can also exist in adifferent oxidation state. hypoiodite is an ion known as IO⁻ which isoxidized more than bromide (Br—).

The present disclosure describes the use of hypoiodite to unexpectedlyimprove the capture of mercury emissions across a wet flue gasdesulfurizer (FGD) in coal-fired flue gas streams or other processingsystem where mercury vapor is present or released. Examples includemunicipal solid waste (MSW) incinerators, medical waste combustors, oreroaster and refineries, and cement kilns.

The scrubbers currently used in the industry include spray towers, jetbubblers, and co-current packed towers as examples. These types of airpollution control devices (APCDs) are provided as examples and are notmeant to represent or suggest any limitation. The hypoiodite may beadded to virgin limestone or lime slurry prior to addition to thescrubber, the recirculation loop of the scrubber liquor, the “lowsolids” return to the scrubber from the scrubber purge stream, demisterwater, make-up water, or the scrubber liquor. Semi-dry FGDs can also beadapted, including spray dryer absorbers (i.e., SDAs), circulating dryscrubbers (CDS) or TURBBOSORP® available from Von Roll. The hypoioditemay be added to semi-dry FGDs so that the hypoiodite contacts mercurypassing through the scrubber.

Typically, the hypoiodite is applied at a ratio of 0.5:1 to 20000000:1weight hypoiodite to weight of mercury being captured. The preferredratio is from 1:1 to 2000000:1 and the most preferred range is from 5:1to 200000:1. In some embodiments, the hypoiodite is prepared by mixingan iodine salt, for example, potassium iodide (KI) with an oxidantsource. The oxidant source may be any oxidant that converts an iodideion (I⁻) to hypoiodite (I—O⁻) such as hypochlorite, e.g. sodiumhypochlorite.

In general, hypoiodite may be introduced into the scrubber and therebyinto the scrubber liquor via several routes. The following will serve asjust some of the variations that are available to introduce thehypoiodite into the scrubber liquor. The scrubber liquor is defined asthe water-based dispersion of calcium carbonate (limestone) or calciumoxide (lime) used in a wet or dry flue gas scrubber to capture SO_(x)emissions. The liquor may also contain other additives such as magnesiumand low-molecular weight organic acids, which function to improve sulfurcapture. One example of such an additive is a mixture of low-molecularweight organic acids known as dibasic acid (DBA). DBA typically consistsof a blend of adipic, succinic, and glutaric acids. Each of theseorganic acids can also be used individually. In addition, anotherlow-molecular weight organic acid that can be used to improve sulfurcapture in a wet scrubber is formic acid. Finally, the scrubber liquorwill also contain byproducts of the interaction between the lime orlimestone and flue gas, which leads to the presence of various amountsof calcium sulfite or calcium sulfate as well as anions such as halides(i.e., chlorides, bromides, and iodides) and other cations such as iron,zinc, sodium, or copper. The scrubber liquor includes but is not limitedto the make-up liquor, return liquor, the reclaimed liquor, virginliquor, and liquor injected directly into flue gases.

Another addition point for the hypoiodite to the wet scrubber is at the“low solids” liquor return. A portion of the liquor is oftencontinuously removed from the scrubber for separating reactionbyproducts from unused lime or limestone. One such means of separationis centrifugation. In this process, the scrubber liquor is separatedinto a “high solids” and “low solids” stream. The high solids stream isdiverted to wastewater processing. The low solids fraction returns tothe wet scrubber and can be considered reclaimed dilute liquor. Thehypoiodite may be added to the reclaimed low solids stream prior toreturning to the scrubber.

Another feed liquor found in the operation of a wet FGD is called“virgin liquor.” Virgin liquor is the water-based dispersion of eitherlime or limestone prior to exposure to flue gas and is used to add freshlime or limestone while maintaining the scrubber liquor level andefficiency of the wet FGD. This is prepared by dispersing the lime orlimestone in water. Here, the hypoiodite can be added either to thedispersion water or to the virgin liquor directly or to the demisterwater.

Finally, some scrubber installations use scrubber liquor and/or water(fresh or recycled) injected directly into the flue gas prior to thescrubber for the purpose of controlling relative humidity of the fluegas or its temperature. The excess liquid is then carried into thescrubber. Here also are two potential addition points for theintroduction of the hypoiodite.

The addition of the hypoiodite can be made in any of these locations,wholly or fractionally (i.e., a single feed point or multiple feedpoints), including but not limited to the make-up water for the lime orlimestone slurry or the scrubber liquor.

In some embodiments, bromide is available as iodine salt or iodic acid(HI) from an upstream process to the scrubber. The bromide salt may bein the form of calcium iodide (CaI₂), sodium iodide (NaI), or otheriodide salts or as a mixture of various iodide salts. Hypoiodite isformed by adding an oxidant to the stream containing the iodine salt togenerate hypoiodite in situ. The oxidant may be added to the scrubberliquor, low solids liquor return, virgin liquor, dispersion water, orother liquid existing during the capture, recovery, and treatmentprocess.

Often, the recovery of desirable ore products involves refining the orefrom materials that contain mercury. For example, phosphate is oftenextracted from phosphorite which contains mercury as a trace element.During refinement of the desirable phosphorous mineral, mercury can beliberated such during fertilizer manufacture. In such cases, the mercurypasses into a scrubber fluid, for example, a sodium-based alkali that isused to capture sulfur dioxide (SO₂). The mercury can be removed usingthe processes described herein.

As another example, gold ore processing often involves roasting the goldore to oxidize and remove sulfide. The gas generated by sulfur burningin the roaster is scrubbed to remove the sulfur dioxide and othercomponents which can be contaminated with mercury. Mercury can beremoved from these off-gases to make the gold processing moreenvironmentally desirable.

Thus, techniques described herein can be used to remove contaminatingamounts of mercury from off-gases arising from various ore processingand ore refineries processing those ores.

The invention is illustrated by the proceeding descriptions and thefollowing examples which are not meant to limit the invention unlessotherwise stated in the claims appended hereto.

EXAMPLES

Testing for elemental mercury oxidation or absorption was performedusing a multiple impinger setup with an inline mercury analyzer. Theinline mercury analyzer for this testing was an Ohio Lumex RA-915Portable Zeeman Mercury Analyzer.

Referring to FIG. 1, a multiple impinger setup (with impingers seriallyconnected: 1 to 2, 2 to 3, 3 to 4, etc.) was used to expose samples withelemental mercury. In Impinger 1, elemental mercury was added (200 ppt,5 mL) and combined with stannous chloride (2 mL) to evolve elementalmercury. In Impinger 2, 30 mL of solution was added. The solution can bea diluted sample, synthetic slurries, test slurries, deionized (DI)water (for calibration and reference) or any combination of the above.In Impingers 3-4, various solutions (30 mL) were added to reduce theamount of volatile material reaching the detector and not affect themercury signal. These various solutions included HNO₃ and NaOH solutionsat concentrations from 0.1 to 1 M. During calibration, these materialsare replaced with the same volume of DI water. In the lastimpinger—Impinger 3, 4 or 5, depending on the system—was left empty tocatch any liquid overflow. The mercury detector was then connected tothe last impinger followed by a carbon trap and pump. The pump drawsambient air from the room where the impingers are located.

The second impinger used for this application was not a typical bottomdraining impinger. Instead, a 100 mL round bottom flask was fitted atthe bottom of the impinger so that the flask could be lowered into aheating bath for variable temperature measurements and was large enoughfor a variety of test solution volumes. The solution was bubbled withgas through a disposable pipette.

Test slurries used were obtained from a commercial limestone forcedoxidation wet flue gas desulfurization scrubber at a coal-firedelectrical generator unit firing eastern bituminous coal. The pH of theslurry is typically between 5.5 and 6.5.

Example 1

Adding potassium iodide (KI) in a 1:10 wt % of KI to hypochlorite insolution generated hypoiodite. FIG. 2 shows a plot of the measuredconcentrations of sodium hypochlorite alone, sodium hypochlorite withpotassium iodide and hypoiodate from the sodium hypochlorite/potassiumiodide solutions associated with the percent of mercury removal from asynthetic slurry comprising 20 wt % CaSO₄. The generation of hypoioditeincreased elemental mercury removal from flue gas when compared tohypochlorite alone.

Mercury removal in FIG. 2 is calculated using the amount of elementalmercury not captured ([Hg⁰]_(NC), mercury detected at the detector)compared to the amount of mercury initially in the system ([Hg⁰]_(I)(Equation 1).

$\begin{matrix}{{{Hg}\mspace{14mu} {Removal}\mspace{14mu} (\%)} = {\left( {1 - \frac{\left\lbrack {Hg}^{0} \right\rbrack_{NC}}{\left\lbrack {Hg}^{0} \right\rbrack_{I}}} \right) \times 100}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Comparative Example 1

To test the saturation of elemental mercury in water, a known amount ofelemental mercury vapor was bubbled through deionized water in a plasticjug using a Mercury Instruments MC-3000 Mercury Calibrator. A mercurygenerator was employed to create vapor phase elemental mercury (29 or270 μg/m³) with a N₂ carrier gas (2.5 L/min). This gaseous mixture wasthen bubbled through deionized water (0.9 L) for a varying amount oftime (1-20 min). A small amount of water was then removed for analysison an Ohio Lumex RA-915 Portable Zeeman Mercury Analyzer.

The retention of elemental mercury in water over time was also testedusing the same testing setup and procedure as above with one addition.After bubbling mercury through the deionized water for a set amount oftime, the mercury ampule was bypassed so that only N₂ gas would flowthrough the deionized water.

Elemental mercury was bubbled through deionized water to determine thesaturation of elemental mercury in a system more similar to the dynamicsystem in a wet flue gas desulfurizer scrubber. The results shown inTable I indicate that the system was driving towards a steady state of˜60 ppt and ˜700 ppt, at 29 μg/m³ and 270 μg/m³ respectively, ratherthan increasing up to the saturation limit of 60 ppb (60,000 ppt) all at25° C. The initial concentrations at short times are higher thanexpected due to an oversaturation of the nitrogen carrier gas in thehead space of the mercury ampoule, causing a burst of elemental mercuryat the beginning of each test. Over time in both the low and highconcentration systems, the concentration of elemental mercury drives toan equilibrium value. The theoretical values in Table I refer to thetotal amount of elemental mercury flow through the testing system basedon concentration, flow rate and time.

TABLE I Elapse Time Hg⁰ in water, (ppt) (min) Theoretical* Actual Gas:29 μg/m³ and 2.5 L/min 1.0 146 235 2.5 309 137 5.0 521 93 10.0 937 6115.0 1,342 58 Gas: 270 μg/m³ and 2.5 L/min 1 349 601 10 6,139 701 2021,139 667

The saturation of elemental mercury in water was driving to equilibriumas governed by Henry's Law (Equation 2 below). Henry's law is defined asHenry's constant (K_(H), 376 atm at 25° C.), mole fraction of elementalmercury in solution (x), and partial pressure of elemental mercury (p,atm). Below in Table II are the theoretical values of elemental mercuryin water based on Henry's Law and the concentration of the gas flowingthrough the system. The values are not exactly the same as the actualmeasured values but are on the same order of magnitude. Thesepredictions are significantly lower than the solubility limit of 60 ppbfor elemental mercury in pure water.

$\begin{matrix}{K_{H} = \frac{p}{x}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

TABLE II Elemental Mercury Concentration Gas Phase Water Phase (ppt)(μg/m³) Actual Theoretical* 29 60 103 270 700 963 0.3 — 2 5.0 — 1816,823 — 60,000

Next, these same solutions were tested for mercury retention orstability by first adding elemental mercury to the water in the samemanner as above and then bypassing the elemental mercury ampoule so thatonly N₂ gas (elemental mercury content of zero) bubbles through thewater for a varying amount of time. This would approximate the effect ofa forced oxidation system in the wet flue gas desulfurizer scrubbers. InTable III, it can be seen that the elemental mercury was quickly removedfrom the deionized water by the pure N₂ gas. This behavior is alsoconsistent with Henry's Law as the elemental mercury in the water phasetransfers to the gas phase, the system continuously shifts in order toreach equilibrium. Elemental mercury was not readily soluble or retainedin deionized water.

TABLE III N₂ flow time (min) Hg (ppt) % retention 29 μg/m³ at 2.5 L/minfor 1 min 0 297 1 174 59% 2.5 71 24% 5 14  5% 29 μg/m³ at 2.5 L/min for10 min 0 76 1 46 61% 2.5 18 24% 5 3.4  4% 270 μg/m³ at 2.5 L/min for 1min 0 601 1 374 62% 2.5 157 26% 5 35.7  6% 270 μg/m³ at 2.5 L/min for 10min 0 701 1 439 63% 5 90 13% 10 5.4  1%

The data in these tables clearly define the problem by demonstratingthat water-based scrubber liquors do not effectively decrease elementalmercury concentration in combustion flue gas.

It is clear from these bench-scale results that the hypoioditesuccessfully and unexpectedly controls the emission of mercury from ascrubber by decreasing the elemental mercury flue gas concentration anddoes so more efficiently than conventional techniques.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the invention and withoutdiminishing its intended advantages. It is therefore intended that suchchanges and modifications be covered by the appended claims.

What is claimed is:
 1. A method for reducing mercury emissions,comprising: providing a gas stream comprising mercury; and passing thegas stream into a scrubber comprising a scrubber liquor and hypoiodite.2. The method of claim 1, wherein the hypoiodite is mixed with acarrying agent selected from: limestone slurry, lime slurry,sodium-based alkali solution, trona-based solution, sodium carbonatesolution, sodium hydroxide solution, and water.
 3. The method of claim2, wherein the carrying agent is limestone slurry.
 4. The method ofclaim 2, wherein the carrying agent is water.
 5. The method of claim 1,further comprising mixing an iodine salt and an oxidant to form thehypoiodite.
 6. The method of claim 5, wherein the oxidant is sodiumhypochlorite.
 7. The method of claim 1, wherein the mercury is fromcombusted coal.
 8. The method of claim 1, wherein the scrubber is a wetscrubber selected from spray tower system, a jet bubblers system, and aco-current packed tower system.
 9. The method of claim 1, wherein thehypoiodite is added to the liquor and then added to the scrubber. 10.The method of claim 1, wherein the hypoiodite is added to the scrubbercontaining the liquor.
 11. The method of claim 1, wherein the hypoioditeis added to a virgin liquor then added to the scrubber.
 12. The methodof claim 1, wherein the hypoiodite is added to a make-up liquor thenadded to the scrubber.
 13. The method of claim 1, wherein the hypoioditeis added to a return liquor then added to the scrubber.
 14. The methodof claim 1, wherein the hypoiodite is added to a reclaimed liquor thenadded to the scrubber.
 15. The method of claim 1, wherein the hypoioditeis added to a liquor injected directly into flue gases then added to thescrubber.
 16. The method of claim 1, wherein the hypoiodite is added toa recirculation loop of the scrubber liquor.
 17. The method of claim 1,wherein the hypoiodite is added to a low solids return to the scrubberfrom a scrubber purge stream.
 18. The method of claim 1, wherein thehypoiodite is added to an aqueous stream introduced into the scrubber.19. The method of claim 1, wherein the hypoidite is added to an aqueousstream introduced into the scrubber, wherein the aqueous stream isselected from a demister and make-up water stream.
 20. The method ofclaim 1, wherein the mercury is from an incinerator, cement kiln, or anore refinery.